An oscillator is a type of circuit that generates a repetitive signal. Oscillators are used in most circuits to generate frequency references, which might be used for processors, digital control circuits, phase locked loops, switched capacitor circuits, and the like. The generated, repetitive signal repeats every time period and operates with a selected frequency and waveform. The waveform can include, for example sawtooth waveforms and sine waves.
One feature oscillators are characterized by is the frequency of their signal. Signals in the audio range can have frequencies ranging from 16 Hz to 20 kHz. Signals in the radio frequency (RF) range typically have frequencies ranging from 100 kHz to 100 GHz. Crystal oscillators are available from kHz up to several 10 MHz.
Another feature oscillators are characterized by is their startup time. This is the time from which the oscillator is off or deactivated until the time when the oscillator is generating a steady, reliable oscillating signal.